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Lesson 4: Classifying triangles

# Worked example: Classifying triangles

Work through sample problems categorizing triangles as scalene, isosceles, equilateral, acute, right, or obtuse.  Created by Sal Khan.

## Want to join the conversation?

• If I have two angles that make no sense like 30, 130 and the third
one is missing how do I find the answer?
• All the angles of a triangle add up to 180 degrees, so if you have two of the measures, you add up the two measures given and then subtract it from 180 to get the third measure. If you want to test if a triangle adds up to 180 degrees, you can cut out a triangle out of paper and then tear of the three corners. Then, on another piece of paper, you draw a straight line because a straight line is 180 degrees. You put all the corners of your triangle on the line and it should fit.
• I'm going to 4th grade this year and I want to improve my reading. And also, I'm looking forward to getting mostly 4’s and 3's on my report card (We grade by 1,2,3,4 with 1 being the worst and 4 being the best.) Any Tips? Thank you very much.
• Practice, practice, practice. Make a study schedule and stick to it. Go over notes you get in class and if you have a hard time understanding something you read or something in class, read it again or ask the teacher to explain it. Ask relevant questions, that always helps. DO NOT fall asleep in class.
To improve in reading, try reading books that challenge you but don't overwhelm you. Experiment a bit to find what books would interest you specifically. If your up to it, try going for books with different styles. By style I mean how its spoken and written. Examples are British vs. American (slight differences in dialect). Or Shakespearean vs. slang (HUGE DIFFERENCE). This helps broaden vocabulary and will definitely help you understand plot and setting better.
Hope this helped. Good luck in fourth grade!!
• Can a equilateral triangle be a scalene triangle?
• A scalene triangle means all sides have a different length. An equilateral triangle means all sides are the same length.
• Obtuse what is it i don't know?
• obtuse angles are angles which measures above 90 degrees and below 180 degrees
• you are pretty we Love you no matter what you pretty like the stars and we love God and we are 4th grade we are pretty we can read we can write and do anything.
• correct that is true we love that
• at I didn't hear what he was saying
• If you ever have trouble understanding what Sal is saying, you can use the transcripts below the videos.
Around he said: "...we can assume that these are drawn to scale, so we can base it on our visual judgement. So I would say that this is obtuse..."
• what the heck is this guys it look I got a bunch of answer
• How would you describe obtuse but also describe other angles with it in one sentence.